All FDA approved antiretroviral drugs fail to completely suppress virus replication. As a result of persistent virus replication and genetic mutation, drug resistance viruses emerge and lead to drug failure and disease progression. Without a standard clinical drug resistance monitoring test, the decision for initiating or switching antiretroviral treatment regimens is complicated. Such a test has the potential to become a critical tool for the management of HIV disease. Recently, new generation phenotypic drug resistance assays have been developed with several advantages over conventional PBMC-based methods. The applicants have developed a primary virus isolate- (PVI) based assay that may have unique advantages. First, the PVI assay is highly sensitive to diverse primary isolates of HIV-1; second, it is able to analyze the entire viral population without selection; third, it can detect minor species of different drug resistant viruses within a virus population; fourth, from a single original virus stock it can evaluate the susceptibility of drugs that effect any level of the virus replication cycle; it has high throughput capability and can quantitatively measure sensitivity and resistance to multiple drugs simultaneously. In this phase I application, they propose to define and standardize the conditions under which the PVI assay can be performed to accurately and reproducibly measure the phenotypic drug resistance properties of primary HIV-1 virus isolates. To accomplish this their specific aims are: (1) to compare the PVI assay against panels of genetically and phenotypically defined resistant viruses, and clinical samples; (2) to define the experimental parameters that optimize the performance of the PVI assay; and define the experimental parameters of the PVI assay that optimize its performance; and (3) to develop a single experimental approach for analyzing HIV-1 resistance against drugs that target any step in the virus life cycle. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE